Lowcal: labeled E4 C2, EFFINERGIE + 2017 and BBCA Excellence.

New Construction

  • Building Type : Office building < 28m
  • Construction Year : 2015
  • Delivery year : 2016
  • Address 1 - street : 65 Les Balcons de l'Amourier 26160 PONT-DE-BARRET, France
  • Climate zone : [Csa] Interior Mediterranean - Mild with dry, hot summer.

  • Net Floor Area : 730 m2
  • Construction/refurbishment cost : 817 000 €
  • Cost/m2 : 1119.18 €/m2

Certifications :

  • Primary energy need :
    -98.7 kWhep/m2.an
    (Calculation method : RT 2012 )
Energy consumption
Economical buildingBuilding
< 50A
51 à 90B
91 à 150C
151 à 230D
231 à 330E
331 à 450F
> 450G
Energy-intensive building

Wood-straw desks, without heating, with positive energy, low carbon and controlled costs: construction of Positive energy, Low tech and low energy gray desks.

LowCal is a building demonstrating our know-how, which is innovative in terms of energy and environmental. All the work invested in this building has been rewarded with several labels at their highest levels: Energy and Carbon labels (E4 C2), BBCA Excellence and BEPOS + Effinergie 2017.LowCal is the first tertiary building to be labeled E4 C2 level. .

See more details about this project


Data reliability

3rd part certified



    Thierry RIESER

Construction Manager


    Thomas RICHARD


    Thermal consultancy agency


    Thierry RIESER - Gérant

    Thermal BE and QEB

    Structures calculist



    Wood structure design office

    Structures calculist



    Concrete structure design office

Contracting method

Separate batches

Owner approach of sustainability

LowCal concept:

  • Low Impact: wood-straw construction, inertia brought by the raw earth, quality of indoor air (healthy materials, ...).
  • Low Tech: building without fixed heating installation, decentralized dual flow ventilation (network limitation), ECS only for showers (occasional use).
  • Low Calories: high insulation, building without fixed heating, control of electricity consumption (lighting at 2 W / m², low-energy computing ...) and of course positive energy for all uses (ie: energy consumption heating, ventilation, lighting, office automation, computer, kitchen area, DHW production of the shower and various uses of electricity); (photovoltaics produces 7 times the total consumption measured by measurement campaign).
  • Local: materials and local businesses, in addition to a rural development dynamic.
  • Low cost: cost of 1 120 € HT / m²SHON (excluding HHT).

This building is a synthesis of the founding principles of the negaWatt approach.

Architectural description

Of a deliberately sober architecture and integrated in the rural village of Pont de Barret, this building reflects by its facade materials its constructive mode wood, married to a traditional lime plaster. Of bioclimatic design, joineries are generous on the southern main facade, while maintaining a natural lighting comfortable on the other orientations. The interior architecture is built around a wide central circulation on both levels, enlivened by the undulation of the mud wall.

If you had to do it again?

After a year in offices and good feedback, Enertech says it is ready to work on the Lowcal concept on a larger scale and adapt to other uses (eg housing). Some points could be reworked such as the improvement of wood shutters (difficult to manipulate), the improvement of acoustics between levels, the integration of electrical networks in a floor (complex with the mud floor) or a work on the water consumption of the toilets (reduction of the timers of the taps).

Building users opinion

Warm, comfortable, bright and pleasant building.

Energy consumption

  • -98,70 kWhep/m2.an
  • 56,00 kWhep/m2.an
  • RT 2012

  • -4,30 kWhef/m2.an
  • Heating: 2.2
    Lighting: 0.6
    VMC: 0.2
    Positive energy building with a Cep = -98.7 kWhep / m².an
    Other (office automation): 2,8
    Photovoltaic production: 55

    The final all-purpose energy consumption is expressed per m² SU, excluding photovoltaic.
    The building has a positive energy of a factor greater than 7 (production 7 times higher than all-purpose consumption)

Envelope performance

  • 0,26 W.m-2.K-1
  • Walls: straw insulation (36cm) + wood wool (5cm)
    Roof: 40 cm cellulose wadding
    Wood joinery with triple glazing with high solar factor

  • 0,59
  • n50

  • 0,53
  • No home automation system. We have adopted a low-tech approach. It is a success ! Users have taken charge of the building and are the actors of its performance and comfort, office by office and summer and winter.


Real final energy consumption


    2 016


    • Others
    • Electric radiator
    • Individual electric boiler
    • No cooling system
    • Free-cooling
    • Double flow heat exchanger
    • Solar photovoltaic
  • 670,00 %
  • Low-tech approach to systems: the building is almost without heating, with a reduced need to less than 5 kW.h / m² by Passive optimization of winter and summer comfort.
    Thus we were able to obtain a radical simplification of the climatic installations, with simple electric radiators (4 kW installed for 620 m² SU!) And no air conditioning.

    Pan South roof covered photovoltaic collectors (24 kWp) of European manufacture.

    Passive performance of the envelope.

Smart Building

    Nothing of that ! Low-tech approach, we did not want to deprive the user of his role as a building actor.

    Low self-consumption rate (7%) because we produce a lot and consume very little!
    On the other hand the rate of self-production (more interesting for a building with positive energy) is 67%, and will be further improved in 2018 by the authorization of walking of the heating only the day (objective:> 85%).

    Great satisfaction of the whole team to be an actor of his comfort, summer as well as winter.

GHG emissions

  • 75,60 KgCO2/m2/an
  • Label E+/C-

  • 605,40 KgCO2 /m2
  • 50,00 an(s)
  • 759,90 KgCO2 /m2
  • The results presented are respectively: USage: Impact Energy + Water / Before use: Eges PCE + Site (which actually contains the replacement and end of life of materials)

Life Cycle Analysis

  • 609,80
  • 51,70 kWhEP
  • Straw-wood constructionGerosourced embroidery: adobe brick made with soil from the groundWooden wool insulation and cellulose waddingOuter and interior wooden joinerySoft linoleum

Water management

  • 100,00 m3

Indoor Air quality

    The measurement campaign also included IAQ. This component was carried out by MEDIECO. See the measurement report in the previous section (eco-materials). The results are overall very good: very low in CO2 and fine particles. A little VOC in vacancy because the ventilation is stopped. This reminds us that even a building using only healthy materials needs to be ventilated so that the air quality is excellent.

Health & Comfort

    Mesures in situ par Médiéco : < 700 ppm de CO2 dans tous les bureaux.

    0 heures au-dessus de 28°C.

    La réalité s'est avérée conforme, le bâtiment reste très agréable en été ! Aucune heure au-dessus de 28°C.

    Good overall acoustical comfort (most of the measurements made by Médiéco are under 45 dBA) Small weakness, however, of the intermediate wooden floor filling raw compressed clay: the joist creates a sound bridge for solid sounds. This has been solved by adding acoustic ceiling in some rooms.


    Wood frame wall - prefabricated straw

    Sud Est Charpente


    Opere strutturali / Struttura - Involucro - Finitura

    Prefabricated timber frame with straw infill

    Good realization and implementation on site

    Zehnder CA70



    HVAC / Ventilazione, Raffrescamento

    Distributed double flow ventilation. The Low-Tech solution to do double flow ventilation without having pipes everywhere, and allow the user to control his ventilation as he controls his lighting: with a simple switch.

    Very appreciated by users.

Construction and exploitation costs

  • 38 000,00
  • 217 000
  • 1 307 000
  • 77 000

Energy bill

  • 806,00

Urban environment

Rural area (Pont de Barret: commune of 600 inhabitants)

Land plot area

1 380,00 m2

Built-up area

22,00 %

Green space


Parking spaces

17 parking spaces not covered and not imperessment
+ bike parking (covered)

Building Environmental Quality

  • Building flexibility
  • indoor air quality and health
  • energy efficiency
  • renewable energies
  • products and materials

Program objective: construction of an office building R + 1 with Garden level.BEPOS on all uses, including the "reimbursement" of gray energy.

  • Low tech design: building without fixed heating system (strictly passive) and with decentralized ventilation desk by office.
  • Overall design bioclimatic type, the materials were chosen for their very low energy gray and are biobased type. The use of VOC (including formaldehyde) materials, except wood, has been banned.

The surroundings will be planted with regional species needing little water.
Building designed to facilitate the possible conversion to residential use for 6 to 8 collective dwellings.
Energy monitoring in progress.
SHON: 757 m² SU: 614 m² Total cost: € 890,000 excluding taxes, ie € 1175 / m²SHON.

Contest categories

Prix tertiaire & industriel

Prix tertiaire & industriel

Trophées Bâtiments Résilients 2020

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    Trophées Bâtiments Résilients 2020